Abstract: To study the application of plasma in techniques of screening, a model simulating slanting the incidence of plane electromagnetic wave into plasma slabs with metal underlay is adopted. The wave has a linear vertical mode of polarization. Using W.K.B solution, the function of wave attenuation, wave frequency and plasma density is deduced. Aiming at different incidence angles, the propagation of electromagnetic wave in three cases of uniform, linear and exponential distribution of plasma density is studied. The results show that the wave attenuation increases with increases in plasma density. The larger the incidence angle, the stronger wave attenuation becomes. For the above-mentioned three plasma distributions, the rules of wave attenuation are similar.